The present invention relates generally to coating devices.
More particularly, it relates to a coating device which has a coating head for applying a coating strip of a flowable coating material on a workpiece surface as well as an application nozzle and a suction nozzle located near one another at a small distance from the workpiece surface. Also, the coating device has a holder for supporting the coating head moveably in at least one direction, and a sensing element which determines the position of the workpiece and provides a corresponding adjustment of the coating head.
A coating device of the above mentioned general type is disclosed for example in the German document DE-GM 93 17 655.4. In this device the sensing element is formed by distance sensors which determine the availability and the position of the workpiece and adjust the coating head through a unit for its movement so that a suitable relative position with respect to the workpiece is provided. A coating head of the above mentioned general type aspirates surrounding air with a suction nozzle, whose edge moves at a relatively small distance from the workpiece surface over the surface. The application nozzle through which air is supplied applies varnish or another flowable material onto the workpiece surface which is located close to it. The suction nozzle is then moved over the applied material to aspirate the excess of the material. The aspirated material is then separated in a suction device from air and recovered or discarded.
The more uniform and small the distance between the edge of the above mentioned nozzles around the opposite workpiece surface, the more uniform the produced coating, and the more accurate can all parameters be controlled. As a result, a minimum material to be applied reaches the suction nozzle.
The sufficiently exact position of the workpiece can be obtained with known distance sensing elements with their suitable design, and a subsequent regulation can control the coating head by means of a movement unit so that it maintains its relative position to the workpiece with any small tolerances, even when it must be twisted or delayed, and thereby it must be moved in alternating relative position on the coating head.
Such regulation was extremely expensive and also susceptible to disturbances. If the regulation is simplified, then loss of the regulating accuracy and in particular the response speed can be caused. A fast responsive, simple regulation has a tendency to immanent regulating oscillations, and the damping of these regulating oscillations worsens the response conditions.
The disturbance sensitivity of such regulation is characteristic especially for small, manual operations in which only a single machine is provided with a coating device. In the case of a failure, a redundant machine can not be used.